Recently, high attention has been widely focused on global environmental issues, and environmentally-friendly motor vehicles equipped with secondary batteries such as electric vehicles and hybrid vehicles have progressively prevailed. These motor vehicles often employ a mode of converting direct current generated from the mounted secondary battery into alternating current through an inverter, and then supplying required electric power to the alternating current motor to provide driving force. Electromagnetic waves are generated due to switching operation of the inverter and the like. Since the electromagnetic waves disturb reception of on-board acoustic equipment or wireless equipment or the like, countermeasures have been taken to house the inverter or the battery, motor or the like together with the inverter in a metallic case to shield the electromagnetic waves (Japanese Patent Application Publication No. 2003-285002 A). Metals with high magnetic permeability have been used as electromagnetic wave shielding materials to shield low frequency electromagnetic fields of 1 MHz or less, in particular low frequency electromagnetic fields of 500 kHz or less.
The electromagnetic waves are emitted not only from the motor vehicles but also from many electric and electronic devices including communication devices, displays and medical devices. The electromagnetic waves may cause erroneous operation of precision devices, and an adverse effect on a human body is further concerned. Therefore, various techniques have been developed for reducing the adverse effects of the electromagnetic waves using an electromagnetic wave shielding material. For example, a copper foil composite obtained by laminating a copper foil and a resin film has been used as the electromagnetic wave shielding material (Japanese Patent Application Publication No. H07-290449 A). The copper foil has an electromagnetic wave shielding property, and the resin film is laminated for reinforcement of the copper foil. An electromagnetic wave shielding structure is also known, in which metal layers are laminated on an inner side and an outer side of an intermediate layer made of an insulating material (Japanese Patent No. 4602680). There is also known a technique for obtaining an electromagnetic wave shielding effect with an improved electromagnetic wave shielding property, light weight property and formability by alternately laminating metal foils and resin layers (Japanese Patent Application Publication No. 2017-5214 A).